In the past years, two independent case control studies have established a correlation between elevated homocysteine levels and Alzheimer's Disease (AD). Since vitamin supplementation with folic acid, vitamin B12, and pyridoxine can lower homocysteine levels, this association raises the exciting possibility that polyvitamin therapy may decrease the incidence of AD. The goal of this proposal is to obtain pilot data necessary to design a large multicenter trial to determine whether vitamin therapy lowers the risk of AD. We plan to do this through the following specific aims: (a) Determine whether fasting or post-methionine load (PML) are best associated with AD. The published studies analyzed homocysteine levels in fasting or randomly drawn serum samples. Since many patients have elevations in homocysteine levels only after a methionine load, and both fasting and PML hyperhomocysteinemia may be associated with dementia, we will determine whether fasting hyperhomocysteinemia, PML hyperhomocysteinemia, or both, are linked to a higher risk of AD. We will also determine whether plasma levels of S-adenosylhomocysteine (SAH) and S- adenosylmethionine (SAM) are nire sensitive markers of functional hyperhomocysteinemia (b) Determine the relative importance of nutritional and genetic factors as determinants of hyperhomocysteinemia. Elevated homocysteine levels result from a complex interplay of genetic and acquired factors, and the link between hyperhomocysteinemia and AD has so far been reported only in Europeans. In an attempt to determine which of these factors is most important in an ethnically and culturally heterogeneous US population, we will administer a nutritional questionnaire and measure vitamin levels in our patients, as well as determine the allelic frequency of the C677T polymorphism of MTHFR, a major genetic determinant of hyperhomocysteinemia. (c) Determine whether vitamin therapy is effective in lowering homocysteine levels in patients with hyperhomocysteinemia. All subjects will be treated sequentially for 12 weeks first with low dose vitamin supplementation, followed by high-dose vitamin supplementation. The effectiveness, compliance rates, and potential side effects of these therapies will be monitored. Each of these specific aims is essential to rationally design a large multicenter trial to determine whether polyvitamin therapy lowers AD risk.